Chemical Insights into Antibacterial N-Halamines

AMP-Mimetic Antimicrobial Polymer-Involved Synergic Therapy with Various Coagents for Improved Efficiency

The misuse of antibiotics contributes to the emergence of multidrug-resistant (MDR) bacteria. Infections caused by MDR bacteria are rapidly evolving into a significant threat to global healthcare due to the lack of effective and safe treatments. Antimicrobial peptides (AMPs) with broad-spectrum antibacterial activity kill bacteria generally through a membrane disruption mechanism; hence, they tend not to induce resistance readily. However, AMPs exhibit disadvantages, such as high cost and susceptibility to proteolytic degradation, which limit their clinical application. AMP-mimetic antimicrobial polymers, with low cost, stability to proteolysis, broad-spectrum antimicrobial activity, negligible antimicrobial resistance, and rapid bactericidal effect, have received extensive attention as a new type of antibacterial drugs. Lately, AMP-mimetic polymer-involved synergic therapy provides a superior alternative to combat MDR bacteria by distinct mechanisms. In this Review, we summarize the AMP-mimetic antimicrobial polymers involved in synergic therapy, particularly focusing on the different combinations between the polymers with commercially available antimicrobials, organic small molecule photosensitizers, inorganic nanomaterials, and nitric oxide.

Halloysite-based inorganic-organic hybrid coatings for durable flame retardant, hydrophobic and antibacterial properties of cotton fabrics

Developing durable protective cotton fabrics (CF) against potential environmental dangers such as fire hazards and bacterial growth remains an imperative but tough challenge. In this study, flame retardant, antibacterial and hydrophobic CF were successfully prepared via two-step coating. The inner coating entailed polyelectrolyte complexes consisting of polyethyleneimine and ammonium polyphosphate with the goal of enhancing the flame retardancy of CF. Halloysite nanotubes (HNTs), a kind of tubular silicate mineral, were creatively modified and introduced to multifunctional coatings to improve flame retardant and antibacterial properties of CF. N-halamine modified HNTs (HNTs-EA-Cl) and polydimethylsiloxane were applied as the outer coating to endow CF with antibacterial and hydrophobic properties and further improve the flame retardancy of CF. After halloysite-based inorganic-organic hybrid coatings, the limiting oxygen index of the treated samples (PAHP-CF) was over 28 %, and the release of heat and smoke was significantly inhibited. PAHP-CF could inactivate 100 % E. coli and S. aureus within 2 h. More importantly, PAHP-CF showed excellent hydrophobicity with a water contact angle of 148° and exhibited great prevention of bacterial adhesion. PAHP-CF exhibited excellent washing durability undergoing 5 washing cycles. This study promotes the development of multifunctional coatings and offers a new way to manufacture multifunctional cotton fabrics.

In Situ Preparation of Chlorine-Regenerable Antimicrobial Polymer Molecular Sieve Membranes

Microbial contamination has profoundly impacted human health, and the effective eradication of widespread microbial issues is essential for addressing serious hygiene concerns. Taking polystyrene (PS) membrane as an example, we herein developed report a robust strategy for the in situ preparation of chlorine-regenerable antimicrobial polymer molecular sieve membranes through combining post-crosslinking and nucleophilic substitution reaction. The cross-linking PS membranes underwent a reaction with 5,5-dimethylhydantoin (DMH), leading to the formation of polymeric N-halamine precursors (PS-DMH). These hydantoinyl groups within PS-DMH were then efficiently converted into biocidal N-halamine structures (PS-DMH-Cl) via a simple chlorination process. ATR-FTIR and XPS spectra were recorded to confirm the chemical composition of the as-prepared PS-DMH-Cl membranes. SEM analyses revealed that the chlorinated PS-DMH-Cl membranes displayed a rough surface with a multitude of humps. The effect of chlorination temperature and time on the oxidative chlorine content in the PS-DMH-Cl membranes was systematically studied. The antimicrobial assays demonstrated that the PS-DMH-Cl membranes could achieve a 6-log inactivation of E. coli and S. aureus within just 4 min of contact time. Additionally, the resulting PS-DMH-Cl membranes exhibited excellent stability and regenerability of the oxidative chlorine content.

Preparation and efficacy of antibacterial methacrylate monomer-based polymethyl methacrylate bone cement containing N-halamine compounds

Introduction

Our objective in this study was to prepare a novel type of polymethyl methacrylate (PMMA) bone cement, analyze its material properties, and evaluate its safety and antibacterial efficacy.

Methods

A halamine compound methacrylate antibacterial PMMA bone cement containing an N-Cl bond structure was formulated, and its material characterization was determined with Fourier transform infrared spectroscopy (FT-IR) and 1H-NMR. The antibacterial properties of the material were studied using contact bacteriostasis and releasing-type bacteriostasis experiments. Finally, in vitro and in vivo biocompatibility experiments were performed to analyze the toxic effects of the material on mice and embryonic osteoblast precursor cells (MC3T3-E1).

Results

Incorporation of the antibacterial methacrylate monomer with the N-halamine compound in the new antibacterial PMMA bone cement significantly increased its contact and releasing-type bacteriostatic performance against Staphylococcus aureus. Notably, at 20% and 25% additions of N-halamine compound, the contact and releasing-type bacteriostasis rates of bone cement samples reached 100% (p < 0.001). Furthermore, the new antibacterial bone cement containing 5%, 10%, and 15% N-halamine compounds showed good biocompatibility in vitro and in vivo.

Conclusion

In this study, we found that the novel antibacterial PMMA bone cement with N-halamine compound methacrylate demonstrated good contact and releasing-type bacteriostatic properties against S. aureus. In particular, bone cement containing a 15% N-halamine monomer exhibited strong antibacterial properties and good in vitro and in vivo biocompatibility.

Mechanical, bioactive, and long-lasting antibacterial properties of a Ti scaffold with gradient pores releasing iodine ions

The ideal bone implant would effectively prevent aseptic as well as septic loosening by minimizing stress shielding, maximizing bone ingrowth, and preventing implant-associated infections. Here, a novel gradient-pore-size titanium scaffold was designed and manufactured to address these requirements. The scaffold features a larger pore size (900 μm) on the top surface, gradually decreasing to small sizes (600 μm to 300 μm) towards the center, creating a gradient structure. To enhance its functionality, the additively manufactured scaffolds were biofunctionalized using simple chemical and heat treatments so as to incorporate calcium and iodine ions throughout the surface. This unique combination of varying pore sizes with a biofunctional surface provides highly desirable mechanical properties, bioactivity, and notably, long-lasting antibacterial activity. The target mechanical aspects, including low elastic modulus, high compression, compression-shear, and fatigue strength, were effectively achieved. Furthermore, the biofunctional surface exhibits remarkable in vitro bioactivity and potent antibacterial activity, even under conditions specifically altered to be favorable for bacterial growth. More importantly, the integration of small pores alongside larger ones ensures a sustained high release of iodine, resulting in antimicrobial activity that persisted for over three months, with full eradication of the bacteria. Taken together, this gradient structure exhibits obvious superiority in combining most of the desired properties, making it an ideal candidate for orthopedic and dental implant applications.

Highly biocidal poly(vinyl alcohol)-hydantoin/starch hybrid gels: A "Trojan Horse" for Bacillus subtilis

HYPOTHESIS

Poly (vinyl alcohol) (PVA) cryogels can be functionalized with n-Halamines to confer biocidal features useful for their application as wound-dressing tools. Their efficacy can be boosted by stably embedding a polymeric bacterial food source (e.g., starch) in the gel matrix. The bioavailability of the food source lures bacteria inside the gel network via chemotactic mechanisms, promoting their contact with the biocidal functionalities and their consequent inactivation.

EXPERIMENTS

The synthesis of a novel hydantoin-functionalized PVA (H-PVA-hyd) is proposed. The newly synthesized H-PVA-hyd polymer was introduced in the formulation of H-PVA-based cryogels. To promote the cryogelation of the systems we exploited phase-separation mechanisms employing either a PVA carrying residual acetate groups (L-PVA) or starch as phase-segregating components. The permanence of the biocidal functionality after swelling was investigated via proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT-IR) microscopy. The activated H-PVA-hyd cryogels have been tested against bacteria with amylolytic activity (Bacillus subtilis) and the outcomes were analyzed by direct observation via confocal laser scanning microscopy (CLSM).

FINDINGS

The cryogels containing starch resulted in being the most effective (up to 90% bacterial killing), despite carrying a lower amount of hydantoin groups than their starch-free counterparts, suggesting that their improved efficacy relies on a "Trojan Horse" type of mechanism.

Multifunctional polymeric guanidine and hydantoin halamines with broad biocidal activity

Prolonged and excessive use of biocides during the coronavirus disease era calls for incorporating new antiviral polymers that enhance the surface design and functionality for existing and potential future pandemics. Herein, we investigated previously unexplored polyamines with nucleophilic biguanide, guanidine, and hydantoin groups that all can be halogenated leading to high contents of oxidizing halogen that enables enhancement of the biocidal activity. Primary amino groups can be used to attach poly(N-vinylguanidine) (PVG) and poly(allylamine-co-4-aminopyridine-co-5-(4-hydroxybenzylidene)hydantoin) (PAH) as well as a broad-spectrum commercial biocide poly(hexamethylene biguanide) (PHMB) onto a solid support. Halogenation of polymer suspensions was conducted through in situ generation of excess hypobromous acid (HBrO) from bromine and sodium hydroxide or by sodium hypochlorite in aqueous solutions, resulting in N-halamines with high contents of active > N-Br or > N-Cl groups. The virucidal activity of the polymers against human respiratory coronavirus HCoV-229E increased dramatically with their halogenation. Brominated PHMB-Br showed activation activity value > 5 even at 1 mg/L, and complete virus inhibition was observed with either PHMB-Br or PAH-Br at 10 mg/mL. Brominated PVG-Br and PAH-Br possessed fungicidal activity against C. albicans, while PHMB was fungistatic. PHMB, PHMB-Br and PAH polymers demonstrated excellent bactericidal activity against the methicillin-resistant S. aureus and vancomycin-resistant E. faecium. Brominated polymers (PHMB-Br, PVG-Br, PAH-Br) were not toxic to the HeLa monolayers, indicating acceptable biocompatibility to cultured human cells. With these features, the N-halamine polymers of the present study are a worthwhile addition to the arsenal of biocides and are promising candidates for development of non-leaching coatings.

Self-Assembled Nanoflowers Realizes Synergistic Sterilization with Photothermal and Chemical Kinetics Therapy

Wounds caused by bacterial infections have become a major challenge in the medical field; however, the overuse of antibiotics has led to increased resistance and bioaccumulation. Therefore, it is urgent to develop an antibacterial agent with excellent antibacterial properties and biosafety. Here, we designed an antibacterial platform that combines photothermal and chemical kinetics therapies. Platinum-cobalt (PtCo) bimetallic nanoparticles (NPs) were first prepared, and then PtCo@MnO2 nanoflowers were obtained by adding MES buffer solution and KMnO4 to the PtCo bimetallic nanoparticle suspension using ultrasound. When light strikes metal NPs, they can strongly absorb the photon energy, resulting in photothermal properties. In addition, Pt and Co were used as the oxidase mimics, and MnO2 was used as the catalase mimic. In summary, the photothermal capacity of PtCo@MnO2 nanoflowers with rough surfaces can effectively disrupt the permeability of the bacterial cell membranes. Further, by catalyzing H2O2, PtCo@MnO2 nanoflowers can generate large amounts of hydroxyl free radicals, which can damage bacterial cell membranes, proteins, and DNA. In addition, MnO2 can effectively alleviate the hypoxic environment of the bacterially infected areas and activate deep bacteria, thus achieving the goal of complete sterilization. The in vitro and in vivo results showed that PtCo@MnO2 displayed excellent antibacterial properties and good biocompatibility.

All-in-one porous membrane enables full protection in guided bone regeneration

The sophisticated hierarchical structure that precisely combines contradictory mechanical and biological characteristics is ideal for biomaterials, but it is challenging to achieve. Herein, we engineer a spatiotemporally hierarchical guided bone regeneration (GBR) membrane by rational bilayer integration of densely porous N-halamine functionalized bacterial cellulose nanonetwork facing the gingiva and loosely porous chitosan-hydroxyapatite composite micronetwork facing the alveolar bone. Our GBR membrane asymmetrically combine stiffness and flexibility, ingrowth barrier and ingrowth guiding, as well as anti-bacteria and cell-activation. The dense layer has a mechanically matched space maintenance capacity toward gingiva, continuously blocks fibroblasts, and prevents bacterial invasion with multiple mechanisms including release-killing, contact-killing, anti-adhesion, and nanopore-blocking; the loose layer is ultra-soft to conformally cover bone surfaces and defect cavity edges, enables ingrowth of osteogenesis-associated cells, and creates a favorable osteogenic microenvironment. As a result, our all-in-one porous membrane possesses full protective abilities in GBR.

High-strength hydrophilic N-halamines chitosan and cellulose nanofibers membranes with repeated bactericidal properties

Direct addition of disinfectants and membrane separation techniques have been common methods to address microbial contamination in water. However, disinfectants may generate toxic by-products, and even minor damage or biofilm formation on filtration membranes can lead to a heightened risk of microbial contamination. Consequently, how to quickly and safely disinfect microbial contaminated water sources remains a huge challenge. In this study, the high-strength broad-spectrum antibacterial CNF/CS composite membrane was fabricated by utilizing cellulose nanofibers (CNF) to reinforce the structure of chitosan (CS). The resulting CNF/CS composite membrane exhibits an impressive tensile strength of 148 MPa and boasts an active chlorine content of 5.29 %. Notably, even after undergoing 50 washing cycles and 10 repeated chlorination procedures, the structural integrity and high active chlorine content of the composite membrane remain preserved, validating its exceptional strength, stability, and chlorine rechargeability. Additionally, the CNF/CS antibacterial materials demonstrate remarkable attributes in terms of rapid sterilization, sustained and consistent release of active chlorine, and efficient inhibition of biofilm formation, demonstrating great potential in efficient, green, and safe sterilization.

Halogenated Antimicrobial Agents to Combat Drug-Resistant Pathogens

Antimicrobial resistance presents us with a potential global crisis as it undermines the abilities of conventional antibiotics to combat pathogenic microbes. The history of antimicrobial agents is replete with examples of scaffolds containing halogens. In this review, we discuss the impacts of halogen atoms in various antibiotic types and antimicrobial scaffolds and their modes of action, structure-activity relationships, and the contributions of halogen atoms in antimicrobial activity and drug resistance. Other halogenated molecules, including carbohydrates, peptides, lipids, and polymeric complexes, are also reviewed, and the effects of halogenated scaffolds on pharmacokinetics, pharmacodynamics, and factors affecting antimicrobial and antivirulence activities are presented. Furthermore, the potential of halogenation to circumvent antimicrobial resistance and rejuvenate impotent antibiotics is addressed. This review provides an overview of the significance of halogenation, the abilities of halogens to interact in biomolecular settings and enhance pharmacological properties, and their potential therapeutic usages in preventing a postantibiotic era. SIGNIFICANCE STATEMENT: Antimicrobial resistance and the increasing impotence of antibiotics are critical threats to global health. The roles and importance of halogen atoms in antimicrobial drug scaffolds have been established, but comparatively little is known of their pharmacological impacts on drug resistance and antivirulence activities. This review is the first to extensively evaluate the roles of halogen atoms in various antibiotic classes and pharmacological scaffolds and to provide an overview of their ability to overcome antimicrobial resistance.

N-Halamine-Based Polypropylene Melt-Blown Nonwoven Fabric with Superhydrophilicity and Antibacterial Properties for Face Masks

Polypropylene melt-blown nonwoven fabric (PP MNF) masks can effectively block pathogens in the environment from entering the human body. However, the adhesion of surviving pathogens to masks poses a risk of human infection. Thus, embedding safe and efficient antibacterial materials is the key to solving pathogen infection. In this study, stable chlorinated poly(methacrylamide-N,N'-methylenebisacrylamide) polypropylene melt-blown nonwoven fabrics (PP-P(MAA-MBAA)-Cl MNFs) have been fabricated by a simple UV cross-link and chlorination process, and the active chlorine content can reach 3500 ppm. The PP-P(MAA-MBAA)-Cl MNFs show excellent hydrophilic and antibacterial properties. The PP-P(MAA-MBAA)-Cl MNFs could kill all bacteria (both Escherichia coli and Staphylococcus aureus) with only 5 min of contact. Therefore, incorporating PP-P(MAA-MBAA)-Cl MNF as a hydrophilic antimicrobial layer into a four-layer PP-based mask holds great potential for enhancing protection and comfort.

Preparation of Rechargeable Antibacterial Polypropylene/N-Halamine Materials Based on Melt Blending and Surface Segregation

Polypropylene (PP) has been widely used in health care and food packaging fields, however, it lacks antibacterial properties. Herein, we prepared the polymeric antibacterial agents (MPP-NDAM) by an in situ amidation reaction between 2,4-diamino-6-dialkylamino-1,3,5-triazine (NDAM) and maleic anhydride grafted polypropylene (MPP) using the melt grafting method. The effects of reaction time and monomer content on the grafting degree of N-halamine were investigated, and a grafting degree of 4.86 wt % was achieved under the optimal reaction conditions. PP/MPP-NDAM composites were further obtained by a melt blending process between PP and MPP-NDAM. With the adoption of surface segregation technology, the content of N-halamine structure on the surface of PP/MPP-NDAM composites was significantly increased. The antibacterial tests showed that the PP/MPP-NDAM composite could achieve 99.9% bactericidal activity against 1.0 × 107 CFU/mL of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) within 10 and 5 min of contact, respectively. The antibacterial effect became more pronounced with the prolongation of chlorinated time, and it could achieve 99.9% bactericidal activity against E. coli within merely 1 min of contact.

Rechargeable Multifunctional Anti-Bacterial AEMs for Electrodialysis: Improving Anti-Biological Performance via Synergistic Antibacterial Mechanism

Constructing a functional layer on the surface of commercial membrane (as a substrate) to inhibit the formation of biofilms is an efficient strategy to prepare an antibacterial anion exchange membrane (AEM). Herein, a rechargeable multifunctional anti-biological system is reported by utilizing the mussel-inspired L-dopa connection function on commercial AEMs. Cobalt nanoparticles (Co NPs) and N-chloramine compounds are deposited on the AEM surface by a two-step modification procedure. The anti-biofouling abilities of the membranes are qualitatively and quantitatively analyzed by adopting common Gram-negative (E. coli) and Gram-positive (S. aureus & Bacillus) bacteria as model biofouling organisms. The optimized membrane exhibits a high stability concerning the NaCl solution separation performance within 240 min. Meantime, the mechanism of the anti-adhesion is un-veiled at an atomic level and molecular dynamics (MD) simulation are conducted to measure the interaction, adsorption energy and average loading by using lipopolysaccharide (LPS) of E. coli. In view of the superior performance of antibacterial surfaces, it is believed that this work could provide a valuable guideline for the design of membrane materials with resistance to biological contamination.

Multifunctional Textiles with Flame Retardant and Antibacterial Properties: A Review

It is well known that bacterial infections and fire-hazards are potentially injurious in daily life. With the increased security awareness of life and properties as well as the improvement of living standards, there has been an increasing demand for multifunctional textiles with flame retardant and antibacterial properties, especially in the fields of home furnishing and medical protection. So far, various treatment methods, including the spray method, the dip-coating method, and the pad-dry-cure method, have been used to apply functional finishing agents onto fabrics to achieve the functionalization in the past exploration stage. Moreover, in addition to the traditional finishing technology, a number of novel technologies have emerged, such as layer-by-layer (LBL) deposition, the sol-gel process, and chemical grafting modification. In addition, some natural biomasses, including chitin, chitosan (CS), and several synthetic functional compounds that possess both flame-retardant and bacteriostatic properties, have also received extensive attention. Hence, this review focuses on introducing some commonly used finishing technologies and flame retardant/antibacterial agents. At the same time, the advantages and disadvantages of different methods and materials were summarized, which will contribute to future research and promote the development and progress of the industry.

Impacts of non-microbial soils on polychloramide disinfectants

The presence of some nonmicrobial chemicals and surfaces, herein called "soils", are known to degrade the performance of biocides, and biocidal assays often include mixtures of materials to mimic the effects of soils. We hypothesized that water-soluble anionic polychloramide biocides were less sensitive to soil interference than cationic polymeric biocides. The relationships between soil composition and antimicrobial polymer biocidal activity were compared for an anionic polychloramide, a cationic polychloramide, and a cationic poly(quaternary ammonium) biocide. The nanoscale soil models individually investigated were polyacrylic acid (PAA), cellulose nanocrystals (CNCs), and bovine serum albumin. The low molecular weight model soils were ammonium chloride, glycine, and succinimide. Three types of soil impacts were identified: 1) sequestration, whereby the soil physically inhibited transport of the biocide to microbes; 2) extraction, whereby the soil reduced or extracted oxidative chlorine, decreasing or eliminating the oxidative chlorine strength; and 3) extraction whereby the biocidal activity increases in the presence of a low molecular weight chemical that carries oxidative Cl from the polymer to the microbes. PAA and CNCs inhibit cationic biocides by sequestration but have little impact on anionic polychloramide. Glycine and BSA extract oxidative chlorine, lowering the biocidal activity of the anionic and cationic polychloramides while not impacting the poly(quaternary ammonium) biocide. Finally, the presence of succinimide increased bacteria deactivation of both anionic and cationic polychloramides. We propose that succinimide extracts oxidative chlorine from the polychloramides and transports it to the bacteria.

Super Antibacterial Capacity and Cell Envelope-Disruptive Mechanism of Ultrasonically Grafted N-Halamine PBAT/PBF Films against Escherichia coli

Antibacterial materials are urgently needed to combat bacterial contamination, growth, or attachment on contact surfaces, as bacterial infections remain a public health crisis worldwide. Here, a novel ultrasound-assisted method is utilized for the first time to fabricate oxidative chlorine-loaded AH@PBAT/PBF-Cl films with more superior grafting efficiency and rechargeable antibacterial effect than those from conventional techniques. The films remarkably inactivate 99.9999% Escherichia coli and Staphylococcus aureus cells, inducing noticeable cell deformations and mechanical instability. The specific antibacterial mechanism against E. coli used as a model organism is unveiled using several cell envelope structural and functional analyses combined with proteomics, peptidoglycomics, and fluorescence probe techniques. Film treatment partially neutralizes the bacterial surface charge, induces oxidative stress and cytoskeleton deformity, alters membrane properties, and disrupts the expression of key proteins involved in the synthesis and transport of the lipopolysaccharide and peptidoglycan, indicating the cell envelope as the primary target. The films specifically target lipopolysaccharides, resulting in structural impairment of the polysaccharide and lipid A components, and inhibit peptidoglycan precursor synthesis. Together, these lead to metabolic disorders, membrane dysfunction, structural collapse, and eventual death. Given the films' antibacterial effects via the disruption of key cell envelope components, they can potentially combat a wide range of bacteria. These findings lay a theoretical basis for developing efficient antibacterial materials for food safety or biomedical applications.

Durable and rechargeable antimicrobial cotton driven by enhanced UV stability and real-time detection of biocidal factors

In this study, graphene oxide/N-halamine nanocomposite was synthesized through Pickering miniemulsion polymerization, which was then coated on cotton surface. The modified cotton exhibited excellent superhydrophobicity, which could effectively prevent microbial infestation and reduce the probability of hydrolysis of active chlorine, with virtually no active chlorine released in water after 72 h. Deposition of reduced graphene oxide nanosheets endowed cotton with ultraviolet-blocking properties, attributing to enhanced UV adsorption and long UV paths. Moreover, encapsulation of polymeric N-halamine resulted in improved UV stability, thus extending the life of N-halamine-based agents. After 24 h of irradiation, 85 % of original biocidal component (active chlorine content) was retained, and approximately 97 % of initial chlorine could be regenerated. Modified cotton has been proven to be an effective oxidizing material against organic pollutants and a potential antimicrobial substance. Inoculated bacteria were completely killed after 1 and 10 min of contact time, respectively. An innovative and simple scheme for determination of active chlorine content was also devised, and real-time inspection of bactericidal activity could be achieved to assure antimicrobial sustainability. Moreover, this method could be utilized to evaluate hazard classification of microbial contamination in different locations, thus broadening the application scope of N-halamine-based cotton fabrics.

Clear polyurethane coatings with excellent virucidal properties: Preparation, characterization and rapid inactivation of human coronaviruses 229E and SARS-CoV-2

Commercial polyurethane (PU) coating formulations have been modified with 1-(hydroxymethyl)-5,5-dimethylhydantoin (HMD) both in bulk (0.5 and 1% w/w) and onto the coatings surface as an N-halamine precursor, to obtain clear coatings with high virucidal activity. Upon immersion in diluted chlorine bleaching, the hydantoin structure on the grafted PU membranes was transformed into N-halamine groups, with a high surface chlorine concentration (40-43μg/cm²). Fourier transform infrared spectroscopy (FTIR) spectroscopy, thermogravimetric analysis (TGA), energy-dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and iodometric titration were used to characterize the coatings and quantify the chlorine contents of the PU membranes after chlorination. Biological evaluation of their activity against Staphylococcus aureus (Gram-positive bacteria) and human coronaviruses HCoV-229E and SARS-CoV-2 was performed, and high inactivation of these pathogens was observed after short contact times. The inactivation of HCoV-229E was higher than 98% for all modified samples after just 30 minutes, whereas it was necessary 12 hours of contact time for complete inactivation of SARS-CoV-2. The coatings were fully rechargeable by immersion in diluted chlorine bleach (2% v/v) for at least 5 chlorination-dechlorination cycles. Moreover, the performance of the antivirus efficiency of the coatings is considered as long-lasting, because experiments of reinfection of the coatings with HCoV-229E coronavirus did not show any loss of the virucidal activity after three consecutive infection cycles without reactivation of the N-halamine groups.

Recent Advances in Superhydrophobic and Antibacterial Cellulose-Based Fibers and Fabrics: Bio-inspiration, Strategies, and Applications

Cellulose-based fabrics are ubiquitous in our daily lives. They are the preferred choice for bedding materials, active sportswear, and next-to-skin apparels. However, the hydrophilic and polysaccharide characteristics of cellulose materials make them vulnerable to bacterial attack and pathogen infection. The design of antibacterial cellulose fabrics has been a long-term and on-going effort. Fabrication strategies based on the construction of surface micro-/nanostructure, chemical modification, and the application of antibacterial agents have been extensively investigated by many research groups worldwide. This review systematically discusses recent research on super-hydrophobic and antibacterial cellulose fabrics, focusing on morphology construction and surface modification. First, natural surfaces showing liquid-repellent and antibacterial properties are introduced and the mechanisms behind are explained. Then, the strategies for fabricating super-hydrophobic cellulose fabrics are summarized, and the contribution of the liquid-repellent function to reducing the adhesion of live bacteria and removing dead bacteria is elucidated. Representative studies on cellulose fabrics functionalized with super-hydrophobic and antibacterial properties are discussed in detail, and their potential applications are also introduced. Finally, the challenges in achieving super-hydrophobic antibacterial cellulose fabrics are discussed, and the future research direction in this area is proposed.

Graphical Abstract

The figure summarizes the natural surfaces and the main fabrication strategies of superhydrophobic antibacterial cellulose fabrics and their potential applications.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42765-023-00297-1.

Totally-green cellulosic fiber with prominent sustained antibacterial and antiviral properties for potential use in spunlaced non-woven fabric production

The worldwide spread of COVID-19 has put a higher requirement for personal medical protective clothing, developing protective clothing with sustained antibacterial and antiviral performance is the priority for safe and sustaining application. For this purpose, we develop a novel cellulose based material with sustained antibacterial and antiviral properties. In the proposed method, the chitosan oligosaccharide (COS) was subjected to a guanylation reaction with dicyandiamide in the presence of Scandium (III) triflate; because of the relatively lower molecular weight and water solubility of the COS, GCOS (guanylated chitosan oligosaccharide) with high substitution degree (DS) could be successfully synthetized without acid application. In this instance, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the GCOS were only 1/8 and 1/4 of that of COS. The introduction of GCOS onto the fiber endowed the fiber with extremely high antibacterial and antiviral performance, showing 100% bacteriostatic rate against Staphylococcus aureus and Escherichia coli and 99.48% virus load reduction of bacteriophage MS2. More importantly, the GCOS modified cellulosic fibers (GCOS-CFs) exhibit excellent sustained antibacterial and antiviral properties; namely, 30 washing cycles had negligible effect on the bacteriostatic rate (100%) and inhibition rate of bacteriophage MS2 (99.0%). Moreover, the paper prepared from the GCOS-CFs still exhibited prominent antibacterial and antiviral activity; inferring that the sheeting forming, press, and drying process have almost no effect on the antibacterial and antiviral performances. The insensitive of antibacterial and antiviral activity to water washing (spunlace) and heat (drying) make the GCOS-CFs a potential material applicable in the spunlaced non-woven fabric production.

Investigating migration potential of a new rechargeable antimicrobial coating for food processing equipment

Antimicrobial coatings are designed to inhibit the growth of pathogens and have been used to reduce foodborne illness bacteria on food processing equipment. Novel N-halamine based antimicrobial coatings are highly advantageous due to their unique properties and low cost, and are being investigated for applications in food safety, health care, water and air disinfection, etc. In this study, we evaluated the chemical safety of a novel N-halamine antimicrobial polymer coating (Halofilm) for use on food processing equipment. Migration tests were performed on stainless steel tiles prepared with four different treatment groups: negative control, positive control, Halofilm coating without chlorination, and Halofilm coating with chlorination. An LC-MS/MS method was developed and validated for four formulation components: polyethylenimine (PEI), Trizma^® base, hydantoin acrylamide (HA) and dopamine methacrylamide (DMA), followed by stability and recovery tests. Migration tests were conducted at 40 °C with three food simulants (10, 50 and 95% ethanol/water) to mimic various food properties, and aliquots of migration extracts were analyzed at 2, 8, 72, 240 and 720 h. In general, measured concentration levels were consistent among simulant types for the four tested chemicals. Chlorinated tiles had non-detects for three analytes (PEI, HA and DMA), and less than 0.05 mg/kg of HA migration over 30 days. A chlorination step could possibly change the measured mass (m/z) hence leading to non-detects in targeted LC-MS/MS. In non-chlorinated tiles, all four compounds were detected during the migration test. This suggests that addition of the chlorination step may have a stabilizing effect on the polymer. Additionally, full scan high resolution mass spectrometry (HRMS) analysis was employed to screen for migration of other extractable and leachable (E&L) chemicals, which led to the identification of eight common E&L chemicals. To our knowledge, this is the first report evaluating chemical migration from an N-halamine antimicrobial polymer coating product.

Rapid and persistent bactericidal cotton fabrics finished facilely with reactive N-halamine

Cotton fabrics (CFs) with persistent and rapid bactericidal capability would be of great significance for daily health protection because CFs are very suitable for the growth and reproduction of microorganisms. Herein, we developed a reactive N-halamine compound, 3-(3-hydroxypropyl diisocyanate)-5,5-dimethylhydantoin (IPDMH), that can be covalently bound to a CF to generate a bactericidal CF after chlorination (CF-DMF-Cl) without damaging its surface morphology. The antibacterial rates of CF-DMF-Cl (0.5 wt% IPDMH) against the gram-negative bacterium Escherichia coli (E. coli) and gram-positive bacterium Staphylococcus aureus (S. aureus) reached 99.99 % and were maintained at 90 % (against E. coli) and 93.5 % (against S. aureus) after 50 laundering cycles. The combination of contact killing and release killing mechanisms by CF-PDM-Cl leads to its rapid and persistent bactericidal activity. In addition, CF-DMF-Cl exhibits adequate biocompatibility, well-maintained mechanical properties, air/water vapor permeability and whiteness. Therefore, the proposed CF-DMF-Cl has great potential applications as a bactericidal CF for use in medical textiles, sportswear, home dressings, and so on.

Demonstrating the In Vitro and In Situ Antimicrobial Activity of Oxide Mineral Microspheres: An Innovative Technology to Be Incorporated into Porous and Nonporous Materials

The antimicrobial activity of surfaces treated with zinc and/or magnesium mineral oxide microspheres is a patented technology that has been demonstrated in vitro against bacteria and viruses. This study aims to evaluate the efficiency and sustainability of the technology in vitro, under simulation-of-use conditions, and in situ. The tests were undertaken in vitro according to the ISO 22196:2011, ISO 20473:2013, and NF S90-700:2019 standards with adapted parameters. Simulation-of-use tests evaluated the robustness of the activity under worst-case scenarios. The in situ tests were conducted on high-touch surfaces. The in vitro results show efficient antimicrobial activity against referenced strains with a log reduction of >2. The sustainability of this effect was time-dependent and detected at lower temperatures (20 ± 2.5 °C) and humidity (46%) conditions for variable inoculum concentrations and contact times. The simulation of use proved the microsphere's efficiency under harsh mechanical and chemical tests. The in situ studies showed a higher than 90% reduction in CFU/25 cm² per treated surface versus the untreated surfaces, reaching a targeted value of <50 CFU/cm². Mineral oxide microspheres can be incorporated into unlimited surface types, including medical devices, to efficiently and sustainably prevent microbial contamination.

Synthesis and evaluation of water-soluble imidazolium salt chitin with broad-spectrum antimicrobial activity and excellent biocompatibility for infected wound healing

Infections caused by bacteria have long constituted a major threat to human health and the economy. Therefore, there is an urgent need to design broad-spectrum antibacterial materials possessing good biocompatibility to treat such infections. Herein, inspired by the good biocompatibility of chitin and antibacterial properties of imidazolium salts, a polysaccharide-based material, imidazolium salt chitin (IMSC), was homogeneously prepared using a facile method with epichlorohydrin as a chemical crosslinker to combine chitin with imidazole to enhance Staphylococcus aureus (S. aureus)-infected wound healing. The characteristics, antimicrobial properties, and biosafety of IMSC were evaluated. The results demonstrated successful grafting of imidazole onto chitin. Furthermore, IMSC exhibited good water solubility, broad-spectrum antimicrobial activity, hemocompatibility, and biocompatibility. Moreover, IMSC enabled complete healing of S. aureus-infected wound in Sprague-Dawley rats within 15 days of application, thus demonstrating that IMSC could reduce wound inflammation and remarkably accelerate wound healing owing to its efficient antibacterial activity and ability to promote collagen deposition in and around the wound area. Therefore, this study provides a promising and potential therapeutic strategy for infected wound healing by synthesizing a water-soluble and broad-spectrum antimicrobial material exhibiting good biocompatibility.

Recent progress of antibacterial hydrogels in wound dressings

Hydrogels are essential biomaterials due to their favorable biocompatibility, mechanical properties similar to human soft tissue extracellular matrix, and tissue repair properties. In skin wound repair, hydrogels with antibacterial functions are especially suitable for dressing applications, so novel antibacterial hydrogel wound dressings have attracted widespread attention, including the design of components, optimization of preparation methods, strategies to reduce bacterial resistance, etc. In this review, we discuss the fabrication of antibacterial hydrogel wound dressings and the challenges associated with the crosslinking methods and chemistry of the materials. We have investigated the advantages and limitations (antibacterial effects and antibacterial mechanisms) of different antibacterial components in the hydrogels to achieve good antibacterial properties, and the response of hydrogels to stimuli such as light, sound, and electricity to reduce bacterial resistance. Conclusively, we provide a systematic summary of antibacterial hydrogel wound dressings findings (crosslinking methods, antibacterial components, antibacterial methods) and an outlook on long-lasting antibacterial effects, a broader antibacterial spectrum, diversified hydrogel forms, and the future development prospects of the field.

From Antibacterial to Antibiofilm Targeting: An Emerging Paradigm Shift in the Development of Quaternary Ammonium Compounds (QACs)

In a previous development stage, mostly individual antibacterial activity was a target in the optimization of biologically active compounds and antiseptic agents. Although this targeting is still valuable, a new trend has appeared since the discovery of superhigh resistance of bacterial cells upon their aggregation into groups. Indeed, it is now well established that the great majority of pathogenic germs are found in the environment as surface-associated microbial communities called biofilms. The protective properties of biofilms and microbial resistance, even to high concentrations of biocides, cause many chronic infections in medical settings and lead to serious economic losses in various areas. A paradigm shift from individual bacterial targeting to also affecting more complex cellular frameworks is taking place and involves multiple strategies for combating biofilms with compounds that are effective at different stages of microbiome formation. Quaternary ammonium compounds (QACs) play a key role in many of these treatments and prophylactic techniques on the basis of both the use of individual antibacterial agents and combination technologies. In this review, we summarize the literature data on the effectiveness of using commercially available and newly synthesized QACs, as well as synergistic treatment techniques based on them. As an important focus, techniques for developing and applying antimicrobial coatings that prevent the formation of biofilms on various surfaces over time are discussed. The information analyzed in this review will be useful to researchers and engineers working in many fields, including the development of a new generation of applied materials; understanding biofilm surface growth; and conducting research in medical, pharmaceutical, and materials sciences. Although regular studies of antibacterial activity are still widely conducted, a promising new trend is also to evaluate antibiofilm activity in a comprehensive study in order to meet the current requirements for the development of highly needed practical applications.

Zwitterion and N-halamine functionalized cotton wound dressing with enhanced antifouling, antibacterial, and hemostatic properties

With emerging needs of wound care management, a multi-functional wound dressing is needed. To prevent infection and reduce patient suffering, antibacterial efficacy against a broad-spectrum of bacteria plus robust antifouling are among the most preferred properties. In this study, a wound dressing was created with antibacterial and anti-fouling capabilities is presented. The approaches used a synthesized tri-functional copolymer comprised of an N-halamine precursor moiety, a marine-inspired surface binding dopamine moiety, and a zwitterionic anti-adhesion moiety bonded onto a commercial cotton gauze. The resulting HaloCare™ wound dressing demonstrated >99.99 % inactivation within 5 min against E. coli and a panel of ESKAPE pathogens plus achieved 98.77 % reduction of non-specific protein binding. HaloCare was also shown to be compatible with hemostatic agents without impacting hemostatic efficacy. HaloCare shows great potential particularly in traumatic injury events as an infection preventing and hemostatic wound management system.

A metalloporphyrin and hydantoin functionalized nanozyme with synergistically enhanced bacterial inhibition

An elaborate design of multimodal antibacterial agents has been revealed to be a promising strategy to address bacterial resistance, originating from the abuse of antibiotics. In this work, we have developed a positively charged and porous material, FePPOP_Hydantoin, as a disinfectant via introducing 1,3-dibromo-5,5-dimethylhydantoin (Hydantoin) and porphyrin iron units into a polymer framework. The extended π conjugated networks of FePPOP_Hydantoin endowed the material with strong near-infrared (NIR) absorption, high density of surface catalytic active centers, superior stability, and reproducibility. FePPOP_Hydantoin exhibits high peroxidase mimetic and photo-Fenton activity, which can catalyze the biologically allowable maximum concentrations of hydrogen peroxide (100 μM) to produce a vast amount of hydroxyl radicals. Simultaneously, the effective electrostatic interaction between the positively charged FePPOP_Hydantoin and the negatively charged bacteria facilitates the binding of FePPOP_Hydantoin on the bacterial membrane, restricting bacteria within the destruction range of hydroxyl radicals and thus making the bacteria more vulnerable. Finally, further close contact between bacteria and Hydantoin units in FePPOP_Hydantoin gave the material an antibacterial efficiency of over 99.999%. Compared with chemical therapy, photo-Fenton therapy, or peroxidase catalytic therapy alone, FePPOP_Hydantoin had a noteworthy multi-amplified antibacterial efficiency. Furthermore, FePPOP_Hydantoin exhibited good biocompatibility and negligible cytotoxicity. The in vivo antibacterial therapy on the Staphylococcus aureus (S. aureus) infected mouse wound model clearly proved the effectiveness of FePPOP_Hydantoin for fighting bacterial infections. This work highlights opportunities for the design of nanozymes with enhanced bacteriostatic activity, providing a new avenue for the construction of novel antibiotics.

Physical Contact-Triggered In Situ Reactivation of Antibacterial Hydrogels

In situ reactivation of hydrogels remains a long-standing key challenge in chemistry and materials science. Herein, we first report an ultraconvenient in situ renewable antibacterial hydrogel prepared via a facile physical contact-triggered strategy based on an ultrafast chlorine transfer pathway. We discover that the as-proposed hydrogel with a programmable 3D network cross-linked by noncovalent bonds and physical interactions can serve as a smart platform for selective active chlorine transfer at the hydrogel/hydrogel interface. Systematic experiments and density functional theory prove that the N-halamine glycopolymers integrated into the hydrogel system work as a specific renewable biocide, permitting the final hydrogel to be recharged in situ within 1 min under ambient conditions. Due to its strength and durability, pathogen specificity, and biocompatibility, coupled with its rapid in situ reactivation, this antibacterial hydrogel holds great potential for in vivo biomedical use and circulating water disinfection. We envision this proposed strategy will pave a new avenue for the development of in situ renewable smart hydrogels for real-world applications.

Dual Coordination between Stereochemistry and Cations Endows Polyethylene Terephthalate Fabrics with Diversiform Antimicrobial Abilities for Attack and Defense

Modification of fabrics by stereochemical antiadhesion strategies is an emerging approach to antimicrobial fabric finishing. However, a purely antiadhesive fabric cannot avoid the passive adhesion of pathogenic microorganisms. To address this issue, borneol 4-formylbenzoate (BF) with a stereochemical structure is introduced into a cationic polymer PEI-modified PET fabric by a simple two-step method. The obtained fabric exhibits remarkable features of high bactericidal activity, excellent resistance to bacterial adhesion, desirable fungal repellent performance, and low cytotoxicity. More impressively, this modified fabric not only effectively reduces microbial contamination during food preservation but also plays a role in avoiding infection and accelerating wound healing in the mouse wound model. The dual coordination between stereochemistry and cations is validated as a viable "attack and defense" antimicrobial strategy, providing an effective guide for diversiform antimicrobial designs.

Lipid Giant Vesicles Engulf Living Bacteria Triggered by Minor Enhancement in Membrane Fluidity

Antibacterial amphiphiles normally kill bacteria by destroying the bacterial membrane. Whether and how antibacterial amphiphiles alter normal cell membrane and lead to subsequent effects on pathogen invasion into cells have been scarcely promulgated. Herein, by taking four antibacterial gemini amphiphiles with different spacer groups to modulate cell-mimic phospholipid giant unilamellar vesicles (GUVs), bacteria adhesion on the modified GUVs surface and bacteria engulfment process by the GUVs are clearly captured by confocal laser scanning microscopy. Further characterization shows that the enhanced cationic surface charge of GUVs by the amphiphiles determines the bacteria adhesion amount, while the involvement of amphiphile in GUVs results in looser molecular arrangement and concomitant higher fluidity in the bilayer membranes, facilitating the bacteria intruding into GUVs. This study sheds new light on the effect of amphiphiles on membrane bilayer and the concurrent effect on pathogen invasion into cell mimics and broadens the nonprotein-mediated endocytosis pathway for live bacteria.

Ultrasound-assisted bromination of indazoles at the C3 position with dibromohydantoin

Bromoaryl compounds have attracted great attention in organic chemistry, especially for the synthesis of pharmaceutical intermediates. Herein, we demonstrated a novel and efficient bromination protocol of indazoles via C-H bond cleavage to give site-specific 3-bromide products that could be further employed as synthetic blocks to prepare drugs. The reaction used DBDMH as a bromine source, tolerated a wide range of indazoles, and finished in 30 min under mild, ultrasound-assisted conditions. Besides, preliminary mechanistic studies revealed that this approach was not a radical process.

Polyvinylidene fluoride multi-scale nanofibrous membrane modified using N-halamine with high filtration efficiency and durable antibacterial properties for air filtration

HYPOTHESIS

Particulate matter (PM) pollution and the coronavirus (COVID-19) pandemic have increased demand for protective masks. However, typical protective masks only intercept particles and produce peculiar odors if worn for extended periods owing to bacterial growth. Therefore, new protective materials with good filtration and antibacterial capabilities are required.

EXPERIMENTS

In this study, we prepared multi-scale polyvinylidene fluoride (PVDF) nanofibrous membranes for efficient filtration and durable antibacterial properties via N-halamine modification.

FINDINGS

The N-halamine-modified nanofibrous membrane (PVDF-PAA-TMP-Cl) had sufficient active chlorine content (800 ppm), and the tensile stress and strain were improved compared with the original membrane, from 6.282 to 9.435 MPa and from 51.3 % to 56.4 %, respectively. To further improve the interception efficiency, ultrafine nanofibers (20-35 nm) were spun on PVDF-PAA-TMP-Cl nanofibrous membranes, and multi-scale PVDF-PAA-TMP-Cl nanofibrous membranes were prepared. These membranes exhibited good PM_0.3 interception (99.93 %), low air resistance (79 Pa), promising long-term PM_2.5 purification ability, and high bactericidal efficiency (>98 %). After ten chlorination cycles, the antibacterial efficiency against Escherichia coli and Staphylococcus aureus exceeded 90 %; hence, the material demonstrated highly efficient filtration and repeatable antibacterial properties. The results of this study have implications for the development of air and water filtration systems and multi-functional protective materials.

N-halamine surface coating for mitigation of biofilm and microbial contamination in water systems for space travel

A copolymer termed HASL produced from monomeric units of 2-acrylamido-2-methyl-1-(5-methylhydantoinyl)propane (HA) and of 3-(trimethoxysilyl)propyl methacrylate (SL) has been coated onto stainless steel and Inconel™ substrates, which upon halogenation with either aqueous oxidative chlorine or bromine, became antimicrobial. It has been demonstrated that the halogenated stainless steel and Inconel™ substrates were effective in producing 6 to 7 log inactivations of Staphylococcus aureus and Escherichia coli O157:H7 within about 10 min, and in prevention of Pseudomonas aeruginosa biofilm formation over a period of at least 72 h on the stainless steel substrates. Upon loss of halogen, the HASL coating could be re-charged with aqueous halogen. The HASL coating was easily applied to the substrates via a simple dip-coating method and was reasonably stable to contact with water. Both chlorinated substrates could be loaded with at least 6 × 1016 oxidative Cl atoms per cm2 and maintained a loading of greater than 1 × 1016 chlorine atoms per cm2 for a period of 3-7 days while agitated in aqueous solution. After loss of chlorine to a level below 1 × 1016 atoms per cm2, the substrates could be recharged to the 6 × 1016 Cl atoms per cm2 level for at least 5 times over a 28 day period. The new antimicrobial coating technology has potential for use in a variety of important applications, particularly for water treatment and storage on spacecraft.

In-situelectrochemical fabrication of Ag@AgCl NW-PET film with superior photocatalytic bactericidal activity

Constructing a composite photocatalyst with efficient charge-transfer pathways is contribute to improving charge separation, which has attracted wide attention owing to its availability in photocatalysis applications. In this work, three-dimensional (3D) silver@silver chloride (Ag@AgCl) network structures are fabricated for photocatalytic inactivation ofEscherichia coli(E. coli) by thein situelectrochemical introducing AgCl shell on the surface of Ag nanowire (NW) networks that are coated on a polyethylene terephthalate (PET) substrate. The obtained Ag@AgCl NW-PET films exhibit good photocatalytic bactericidal activity againstE. coliunder simulated Sunlight irradiation, mainly due to their efficient charge-transport channel constructed by the Ag NWs network. It is worth noting that the content of converted AgCl shell is positively correlated with their photocatalytic bactericidal efficiency. The experimental results also demonstrate that the synergistic contribution of Ag⁺sustained release, rough surfaces and energy band structure optimization in photocatalytic sterilization. Besides, the prepared Ag@AgCl NW-PET film can be recycled, and the photocatalytic sterilization efficiency can still keep above 99% after three cycles. This work might provide new and more diverse opportunities for the development of excellent charge-transport, recyclable photocatalysts for photocatalytic sterilization.

Surface modification of titanium with antibacterial porous N-halamine coating to prevent peri-implant infection

Peri-implant infection remains one of the greatest threats to orthopedics. The construction of bone implants with good antibacterial and osteogenic properties is beneficial for reducing the risk of implant-related infections and healing bone defects. In this study, N-halamine coating (namely N-Cl) was grafted onto alkali-heat treated titanium (Ti) using polydopamine to endow Ti-based orthopedic implants with strong bactericidal activity. Surface characterization revealed that the N-Cl coating has porous structure loaded with active chlorine (Cl⁺). The N-Cl coating also provided micro/nano-structured Ti surfaces with excellent antibacterial ability via transformation between N-H and N-Cl, and approximately 100% disinfection was achieved. Furthermore, the as-prepared N-Cl coating exhibited good biocompatibility and osteogenesis abilityin vitro. These results indicate that applying N-Cl coatings on Ti could prevent and treat peri-implant infections.

A Critical Review on Chemical Speciation of Chlorine-Produced Oxidants (CPOs) in Seawater. Part 1: Chlorine Chemistry in Seawater and Its Consequences in Terms of Biocidal Effectiveness and Environmental Impact

Seawater chlorination has three main industrial uses: disinfection of water and installations, control of biofouling, and preventing the transport of aquatic invasive species. Once in contact with seawater, chlorine reacts rapidly with water constituents (e.g. bromide ions, ammonia, and nitrogen-containing compounds) to form a range of oxidative species (e.g. bromine and N-haloamines), termed "chlorine-produced oxidants" (CPOs) or "total residual oxidants" (TRO). The chemical nature of CPOs and their concentration are a function of two categories of parameters related to treatment modality (e.g. chlorine dose) and water quality (e.g. temperature, pH, ammonia concentration, and organic constituents). The chlorination process may result in continuous or intermittent releases of CPOs in seawater. The reactivity and potential ecotoxicity of CPO species largely depend on their physical and chemical properties. Therefore, evaluation of the biocidal effectiveness of chlorination and its potential impacts requires not only determining the sum of CPOs (via a bulk parameter), but also their chemical speciation. The aim of this article - which is the first of a trilogy dedicated to the chemical speciation of CPOs in seawater - is to provide an overview of current knowledge about chlorine chemistry in seawater and to discuss the biocidal efficacy and the environmental fate of resulting CPOs. The 2nd and 3rd articles delineate a comprehensive and critical review of analytical methods and approaches for the determination of CPOs in seawater.

Synthesis of Polylactic Acid Oligomers for Broad-Spectrum Antimicrobials

Infectious microbial diseases are a major public health hazard, calling for more innovative antimicrobials. Herein, polylactic acid (PLA) oligomers have been explored and reported as a bio-safe and eco-friendly functional antimicrobial agent against pathogens, such as viruses (H1N1, H3N2, and SARS-CoV-2), bacteria (E. coli, S. aureus, K. pneumoniae, MRSA), and fungi (C. albicans). The PLA oligomers were prepared by direct catalyst-free condensation polymerization of l-lactic acid monomers and characterized by FT-IR and 1H-NMR. The antiviral results demonstrate that PLA oligomers possess robust (inhibiting rate > 99%) and rapid (<20 min) antiviral activity against two pandemic ssRNA viruses, including influenza A virus (IAV) and coronavirus (CoV). Furthermore, the PLA oligomers exhibit high antibacterial activities against both Gram negative (G−) and Gram positive (G+) bacteria. The PLA oligomers also perform efficiently in killing a large amount of C. albicans as high as 105 cfu/mL down to zero at the concentration of 10 mg/mL. Thus, the broad-spectrum antimicrobial activity endowed the PLA oligomers with a promising biocidal option, except antibiotics in a wide range of applications, such as medical textiles, food preservation, water disinfection, and personal hygiene, in light of their unique biodegradability and biocompatibility.

Modeling the Impact of Polychloramide Solution Properties on Bacterial Disinfection Kinetics

Anionic water-soluble polychloramide biocides are of interest because, compared to conventional cationic antimicrobial polymers, anionic biocides are less likely to be sequestered or deactivated by contact with non-microbial soil. Although electrostatics can prevent anionic polymers from adsorbing on microbes, water-soluble polychloramides appear to transfer oxidative chlorine during transient contacts between polymer chains and microbe surfaces. The Chick-Watson model of disinfection kinetics has been modified to account for the contributions of polychloramide molecular weight (MW) and the polychloramide configuration in solution estimated from the overlap concentration, C*, below which dilute polymer chains exist as discrete objects in solution. The key assumption in the modeling was that the transfer rate of oxidative chlorine from polychloramide chains to microbe surfaces impacts the disinfection kinetics. Because both C* and MW are measurable, the polymer-modified Chick-Watson (PCW) model has one less unknown parameter than the two-parameter Chick-Watson equation. The PCW model predicts that lower MW polymers are more effective biocides compared with high MW counterparts. Additionally, polymers with more compressed configurations in solution are more effective biocides. Experimental evidence supports these conclusions. Based on the estimated time scale of bacteria/polymer collisions compared with disinfection kinetics, arguments are made that bacteria surfaces must be contracted many times by polychloramide chains to achieve sufficient Cl transfer to deactivate bacteria.

Novel chlorine-extending polymer coating with prolonged antiviral activity against SARS-CoV-2

We previously reported a novel polymeric surface coating, namely HaloFilm^TM , that can immobilize and extend the antimicrobial activity of chlorine on surfaces. In this study, we demonstrated the continuous antiviral efficacy of HaloFilm^TM when applied on stainless steel and cotton gauze as two representative models for non-porous and porous surfaces against SARS-CoV-2. Forty-eight hours post HaloFilm application and chlorination, and 2 hours post the viral challenge, the inoculum titer was reduced by 2.25±0.33 and ≥4.36±0.23 log₁₀ TCIDA₅₀ on non-porous and porous surfaces, respectively. The half-life of the virus was shorter (13.86 min) on a HaloFilm^TM -coated surface compared to what has been reported on copper (46.44 min).

Addressing a future pandemic: how can non-biological complex drugs prepare us for antimicrobial resistance threats?

Loss of effective antibiotics through antimicrobial resistance (AMR) is one of the greatest threats to human health. By 2050, the annual death rate resulting from AMR infections is predicted to have climbed from 1.27 million per annum in 2019, up to 10 million per annum. It is therefore imperative to preserve the effectiveness of both existing and future antibiotics, such that they continue to save lives. One way to conserve the use of existing antibiotics and build further contingency against resistant strains is to develop alternatives. Non-biological complex drugs (NBCDs) are an emerging class of therapeutics that show multi-mechanistic antimicrobial activity and hold great promise as next generation antimicrobial agents. We critically outline the focal advancements for each key material class, including antimicrobial polymer materials, carbon nanomaterials, and inorganic nanomaterials, and highlight the potential for the development of antimicrobial resistance against each class. Finally, we outline remaining challenges for their clinical translation, including the need for specific regulatory pathways to be established in order to allow for more efficient clinical approval and adoption of these new technologies.

Organic-free growth of gold nanosheets inside 3D bacterial cellulose as highly efficient and robust antibacterial biopolymers

Without any chemical agent, gold nanosheets (AuNSs) were controllable synthesized through a facile photo-induced reduction within bacterial cellulose (BC) biopolymers. Compared with traditional polymers, AuNSs modified BC biopolymers (AuNSs@BC) biopolymers exhibited similar levels of softness, ductility, and better tensile strength. The in situ constructing of AuNSs@BC biopolymers was demonstrated to provide great reusability and antibacterial activities and towards both of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The optimized AuNSs@BC biopolymers remain at least 95% antibacterial activities after three cycles. The facile and shape-controlled synthesis of AuNSs@BC biopolymers is believed to be useful for the design and application of biomass-based medical dressing.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10853-022-07273-x.

EGCG-coated silver nanoparticles self-assemble with selenium nanowires for treatment of drug-resistant bacterial infections by generating ROS and disrupting biofilms

Bacterial infections pose a serious threat to human health, and the development of new antibiotics has not kept pace with the development of bacterial resistance. Therefore, there is an urgent need to design antibiotic-like nano-formulations that break through bacterial resistance mechanisms. In this work, we successfully synthesized a safe and effective antibacterial nano-formulation of Se@Ag@EGCG by self-assembly of epigallocatechin gallate (EGCG)-coated silver nanoparticles (Ag) on the surface of selenium nanowires (Se). Thein vitrobacteriostatic results showed that 40μg ml^-1Se@Ag@EGCG had significant antibacterial activity against drug-resistantStaphylococcus aureus(S. aureus) andEscherichia coli(E. coli) by destroying the formation of bacterial biofilm, promoting the production of high concentration reactive oxygen species and destroying bacterial cell wall. In addition, the results ofin vivoantibacterial experiments showed that subcutaneous administration of 10 mg kg^-1of Se@Ag@EGCG could promote wound healing by reducing apoptosis and inflammatory responses in infected wounds. It is worth mentioning that the reduced and modified Se@Ag@EGCG by this natural product has negligiblein vivotoxicity. This development strategy of nano-antibacterial materials, which breaks through the drug resistance mechanism, provides new ideas for the development of drugs for drug-resistant bacterial infections.